growth of the epiblast and mesoblast derivatives of the brain, others to a disharmony in the development of related associated brain segments; in the severer cases both elements are combined. It is not difficult to perceive the relation existing between a defective brain weight, paucity of the gyri, deficiency of properly developed cortical cells and such an elementary form of mental aberration as simple imbecility. The subject of the relation between structure and function gains in interest when we leave this domain of simple mental weakness to analyse the relation between structural defects and the positive symptoms of insanity and degeneracy--that is, moral perversion, mental obliquity, delusions, and morbid impulses. Such symptoms are not limited to the higher forms of the degenerate series; they occur, though less constantly and less markedly, in the lower forms. C. K. Mills,[249] of Philadelphia, on examination of imbecile, paranoiac, and criminal brains, found atypical asymmetry as to gyral and fissure development present. The features of this atypical asymmetry were the existence of a Sylvian fissure shorter on one side than the other, both absolutely and comparatively, and also a more vertical direction of the fissure on one side than on the other, greater exposure of the insula on one side with marked differences in the development of its fissures and gyri, confluence of the central fissure with the Sylvian on one side only, and great tortuosity or bridging of the former fissure in one hemisphere, unusual narrowness, straightness of complication of the precentral or postcentral gyrus on one side; marked difference in the simplicity of complexity of the frontal lobes, great simplicity of the orbital surface on one side, differences in the parietal fissure as to length and interruption, a smaller parietal or marginal or angular gyrus on one side, very great difference in the degrees of confluence and interruption of the fissures in general, exceeding great length vertically of the supertemporal or parallel fissure on one side, unusual differences in the size of the precuneus and cuneus.